1. Field of the Invention
This invention resides in the field of process equipment used in the treatment of materials in liquid media by ultrasound.
2. Description of the Prior Art
The use of ultrasound in accelerating the rates of chemical reactions is well known. Examples of publications that describe chemical uses of ultrasound are Suslick, K. S., Science, vol. 247, p. 1439 (1990), and Mason, T. J., Practical Sonochemistry, A User""s Guide to Applications in Chemistry and Chemical Engineering, Ellis Norwood Publishers, West Sussex, England (1991). Of the various sonicating systems that have been developed, those known as xe2x80x9cprobexe2x80x9d-type systems include an ultrasonic transducer that generates ultrasonic energy and transmits that energy to an ultrasonic horn for amplification.
In use, ultrasonic horns are susceptible to wear and erosion, particularly when their use requires contact with an aqueous liquid reaction medium. Once erosion develops, the horns tend to lose their effectiveness and their efficiency in amplifying the ultrasonic energy drops. To minimize this loss, ultrasonic horns are typically made of steel, titanium alloys, or aluminum alloys. Each has its limitations, however. The high density of steel requires relatively high power to excite the horn and therefore a high input source for electric power. Aluminum and aluminum alloys are less dense, but more susceptible to stress fractures from the ultrasonic vibrations. Titanium alloys are preferred materials of construction, but are still susceptible to corrosion and loss of efficiency.
It has now been discovered that the corrosion rate and the rate of loss of energy efficiency of a titanium-based metal ultrasonic horn when used in an aqueous environment can be reduced significantly by using a silver-based metal at the exposed end of the horn. This can be accomplished either by depositing a silver-based metal on the end surface, by securing a cap of silver-based metal to the end or the end surface of the horn, or by constructing rod portion of the horn with a titanium shell and a silver-based metal core with the core exposed at the end surface. The silver-based metal will occupy either a portion of the end surface, preferably a central portion, or the entire end surface. A horn with silver-based metal at its exposed end can be used for extended periods of time with substantially no decline in its ability to amplify the ultrasonic energy produced by the transducer.